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Beryllium-10 dating of the Foothills Erratics Train in Alberta, Canada, indicates detachment of the Laurentide Ice Sheet from the Rocky Mountains at ~15 ka

Published online by Cambridge University Press:  17 April 2019

Martin Margold Open the ORCID record for Martin Margold [Opens in a new window] ,
John C. Gosse ,
Alan J. Hidy ,
Robin J. Woywitka ,
Joseph M. Young  and
Duane Froese
Martin Margold*
Affiliation:
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Department of Physical Geography and Geoecology, Charles University in Prague, Faculty of Science, 128 43 Praha 2, Czech Republic
John C. Gosse
Affiliation:
Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
Alan J. Hidy
Affiliation:
Centre for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
Robin J. Woywitka
Affiliation:
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
Joseph M. Young
Affiliation:
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
Duane Froese
Affiliation:
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
*
*Corresponding author at: e-mail address: [email protected] (M. Margold).
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Abstract

The Foothills Erratics Train consists of large quartzite blocks of Rocky Mountains origin deposited on the eastern slopes of the Rocky Mountain Foothills in Alberta between ~53.5°N and 49°N. The blocks were deposited in their present locations when the western margin of the Laurentide Ice Sheet (LIS) detached from the local ice masses of the Rocky Mountains, which initiated the opening of the southern end of the ice-free corridor between the Cordilleran Ice Sheet and the LIS. We use 10Be exposure dating to constrain the beginning of this decoupling. Based on a group of 12 samples well-clustered in time, we date the detachment of the western LIS margin from the Rocky Mountain front to ~14.9 ± 0.9 ka. This is ~1000 years later than previously assumed, but a lack of a latitudinal trend in the ages over a distance of ~500 km is consistent with the rapid opening of a long wedge of unglaciated terrain portrayed in existing ice-retreat reconstructions. A later separation of the western LIS margin from the mountain front implies higher ice margin–retreat rates in order to meet the Younger Dryas ice margin position near the boundary of the Canadian Shield ~2000 years later.

Keywords

Laurentide Ice SheetCordilleran Ice SheetRocky Mountains10Be exposure datingdeglaciation
Type
Research Article
Information
Quaternary Research , Volume 92 , Issue 2 , September 2019 , pp. 469 - 482
Creative Commons
This is a work of the U.S. Government and is not subject to copyright protection in the United States
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Copyright © University of Washington. Published by Cambridge University Press, 2019

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